Wide band antenna



April 29, 1941. N. E. LINDENBLAD 2,239,724

WIDE BAND ANTENNA Filed May 18, 1938 8 Sheets-Sheet l WA VELENGTH IN CM.

INVENTOR. N/LS E. LINDEN BLAD ATTORNEY.

N. E. LINDENBLAD WIDE BAND ANTENNA Filed may 18, 1958' 8 Sheets-Sheet 2 n INVENTOR. N/L E. L/NDENBLAD f/@MM ATTORNEY.

N. E. LINDENBLAD April 29, 19410 WIDE BAND ANTENNA Filed May 18, '1938 8 Sheets-Sheet 3 fre/Vf. 0M.

fas. 189 y WA VELE/V67?! IN CM WA VELE/V677! /N C' M.

WAVELENGT H IN CM.

INVENTOR. NLS E, LNDENBLAD ATTORNEY.

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Filed May 18, 1938 8 Sheets-Sheet INVENTOR. LS .LINDENBLD BY /vm/-M/ ATTORNEY.

April 29, 1941. N. E. LxNDENBLAD WIDE BAND ANTENNA Filed May 18, 1938 8 Sheets-Sheet 5 INVEN TOR. N/LS E lA/'DEN BLA D M42/Ww A TTORNEY.

April 29, 1941. N; E. LINDENBLAD WIDE BAND ANTENNA Filed may 18, 195B 8 Sheets-Sheet 6 T0 ONE PHASE 0F VIDEO TRANSMITTER .MW N.

70 AUD/0 TRANSM/T TER INVNTOR.

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w. N m T T A Dl/57+ PULL 0U TPU T VIDEO TRANSMITTER APril `29, 1941- N. E. LINDENBLAD 2,239,724

' WIDE BAND ANTENNA 8 Sheets-Sheet 8 Filed May 18, 1938 ATTORNEY.

Patented Apr. 29., 1941 WIDE BAND ANTENNA Nils E. Llndenblad, Port Jefferson, N. Y., assigner to Radio Corporation of America, a corporation of Delaware Application May is, 193s, serial No. 208,573

(ci. 25o-s3) si claims.

'I'his invention relates to a short wave antenna.

An object of this invention is to provide an antenna suitable for the transmission of an extremely wide band of frequencies. My antenna is, accordingly, especially suitable for the transmission of high quality television signals.

Another object of this invention is to provide a practical radiator having a substantially at characteristic over a wide range of r frequencies making it thereby especially suited for television transmission.

Another object of this invention is to provide an antenna adapted to transmit, with relatively low and relatively constant circuit loss over a wide range of frequencies horizontally polarized waves.

A further object of this invention is to provide an antenna having a low factor of reflection over a wide band of frequencies.

Still a further object of this invention is to provide an antenna having the above characteristics and which, in addition, shall be mechanically safe and suitable for use on tall buildings or e towers.

A further object of this invention'is to provide an antenna which will be simple, mechanically strong, and entirely metallic in` construction.

Still another object of this invention is to provide an antenna which will be entirely electrically grounded for protection against lightning, and which, though grounded, will not have its operation as an elective and eilicient high frequency antenna, impaired or otherwise affected.

Briefly, this invention comprises an antenna comprising one or more conductors having a diameter which is a large fraction of lthe length of the working wave. As an example, in accordance with this invention conductors having a diameter of from 15 centimeters (maximum diameter of one component) to 26 centimeters vention the diameter of the antenna, as a whole,

is arranged to decrease with an increase in distance from the neutral voltage pla-nes of the antenna.

The antenna as constructed according to one form of this invention, is connected to the associated apparatus by means of a concentric transmission line, the transmission line being gradually expanded to make a smooth transition between the comparatively small diameter transmission line and the large diameter antenna components.` The ratio between the diameters of the inner and outer conductors of the transmission line is kept constant in the transition section in order to prevent any material change in the characteristic line surge impedance.'

In order to maintain a constant ratio of resistance to low reactance in one modification this antenna.v is arranged so that the shell of the concentric transmission line connected thereto comprises a portion of the radiator with the enlarged central conductor as the other portion. The integrated length of the combination is in the order of a quarter of the operating wave length.

'I'he antenna,' as a whole, is preferably fed at the transition point between the sleeve and the central extension portion of .each quarter wave radiating section. This makes the sleeve portion of the antenna a parallel reactance of predominant inductive value and the center conductor extension a series reactance of predominant capacitive value.

By electrically connecting a predetermined portion of the center conductor extension to the shell portion some irregularities in phaserelationship between the diierent portions of the antenna are avoided and metallic grounding of the entire antenna is permissible. In order to compensate for the shunting inductance caused by this connection a compensating shunt capacity may be provided. One way this may be done is by decreasing the ratio between the diameters of the outer and inner conductors of the transmission line along the length of the tapered transitional portion between the transmission line proper and the antenna.

The foregoing principles of this invention may be applied to a turnstile antenna having a plurality of horizontal quarter wave sections arranged around a central point and mechanically and electrically connected at the center. These radiators may be energized in the proper phase relationship to generate a rotating electrical field, as disclosed in Patent No. 2,086,976, issued to G. H. Brown, July 13, 1937.` Also, a plurality of turnstiles may-be arranged one above the other and energized by diierent signals. According to this aspect of this invention opposite phase rotation between the successive turnstiles may be provided in order to reduce coupling therebetween.

Furthermore, a turnstile and a loop antenna are provided arranged in parallel horizontal planes with their axes on a common perpendicular axis. The loop antenna may be constructed of al plurality of folded dipole sections bent into a circle.

A more complete understanding of this invention may be had by references to the following detailed description a-nd the accompanying drawings. In the latter, Figures 1, 3, 5, 7, 8, 10, l2, 14, 15, 16and 18 illustrate different forms of this invention and Figures 2, 4, 6, 9, 11, 13 and 23 are curves explanatory of the characteristics of antennas constructed according to this invention. Figure 17 is a diagram showing the instantaneous current relationships between two portions of a turnstile antenna connected according to this invention. Figures 19 and 20 are gures further illustrative and explanatory of the principles of this invention, while Figures 21 and 22 show preferred connections ior connecting the antenna to the transmitter. Figures 24 and 25 illustrate diagrammatically the method of connecting a plurality of video and audio' transmitters to a single antenna of the invention. Figures 26 and 27 illustrate further modifications of the invention.

Referring to Figure 1, reference numeral II indicates the radiating portion of a quarter wave antenna so-called because its length is physically substantially equal to one-quarter of the length of the operating wave. Radiator II is fed by a concentric cable or transmission line comprising casing I3 and central conductor I4. The transmission line casing I3 is terminated at the base of the antenna and electrically connected to a grounded conducting surface, body, or sheet, I2, such as a metal roof or the steel framework of a. building or tower. The conductor Il is of substantially larger diameter than is customary in the prior art. In one embodiment which is used with a wavelength of the operating wave of the order of 175 centimeters, the diameter was of the order of one inch. The surge impedance of the transmission line is preferably made of the order of 36 ohms which is the theoretically expected impedance at the base of a quarter wave radiator.

In determining the reec-tion of this antenna and plotting the reflection factor against; the irequencies, curve a in Figure 2 is obtained. This reflection lfactor is measured on the transmission line and is derived from the ratio between the maximum and minimum current appearing at different points along the transmission line. In short, this factor is the ratio of a current node to antinode as measured along the line. Reflection may be caused in several ways. First, the loading resistance may not correspond to the surge impedance of the line feeding it; second, the loading impedance may be correct but a reactive component may be present; third, both these causes may be combined. The quantity and kind of reliectionA present is determined from the position of maxima or minima of the standing wave component on the line. If it is desired to obtain an expression cf the reflection in percentage terms, taking a specific example where the ratio of maximum to minimum voltage is 1.1 to 1, the percentage reflection is obtained from the following expression:

% reflection ldirectly as the ratio of maximum to minimum voltage and not as percentages.

Using a, smaller conductor for radiator Il, A;

of an inch for example, curve b of Figure 2 is obtained. As can readily be seen, while neither of these radiators presents a perfect impedance match to the transmission line, the larger diameter radiator has a wider eiective band width v than the other.

Modifying the radiator, as shown in Figure 3, but using the same 36 ohm transmission line1 by substituting a tapered radiator portion 2l enables obtaining a desirable impedance match for a rather restricted band of frequencies or wave lengths, as shown by the sharp minimum point of the curve in Figure 1i. Therefore; while a good impedance match is obtained over a very narrow band of frequencies, the band width for this modiiication. is not materially improved and will be found too narrow for a high quality, wide frequency band television transmission.

It therefore follows from the previous discussion that the method of energization of the anrtenna has a very important effect on the band width and it is to this problem that the remainder of this specification provides a highly satisfactory solution.

I have discovered that a radiator in which the shell of the transmission line forms an active part of 'the radiator itself oiers a variety of advantages. The modification of this invention, constructed as in Figure 5 wherein the shell portion of the concentric transmission line is extended beyond the ground connection sheet I2 for a portion of the distance of the antenna, resuits in an improved frequency characteristic as shown in Figure 6. By using this construction a more perfect impedance match is obtained for much wider bands of frequencies, particularly when used in conjunction with the teachings of Figures 1 and 2 prescribing conductors of large diameters. The center radiator 3| in Figure 5 continuing beyond the shell has a series reactance characteristic of predominant capacitive value for the portion B While the lower portion A of this composite radiator formed by the outside of the projecting shell has a parallel reactance characteristic of inductive predominance. These two elements in series form a circuit having a wider or improved band width characteristic. As can be seen in Figure 6, the typical reflection curve is much broader and flatter over a wide range of frequencies j--j and has a small hump in the center. This hump is natural since it is the result of a combination of :two effects which can only be perfect for definite frequencies.

In addition to the compensating advantages already mentioned, another and exceedingly important advantage is that by proportioning the center line and the sleeve extensions the antenna can be made to match any concentricY line. For Various diameters of conductor 3l the ratio between lengths A and B for optimum band width ,f--f, that is, maximum band Width with a low factor of reiiection does notl vary greatly for a given line or matching impedance. Over a range of line impedances varying from 70 to 1,45 ohms it appears that a line impedance of ohms may well be chosen as giving very satisfactory band width. For constant radiator diameters the mtio between lengths A and B (Figure 5) increases as the line impedance is increased. However, that is not the only factor which iniiuences the length of A and B (Figure 5) since this ratio can be modiiied if the external dimensions and shapes of :the conductors 3l and I3 are correspondingly altered. The aim is to approach a combination of the capacitative eiect of conductor 3| and inductive ellect of shell 33 such that the for as wide a frequency band as possible. In the foregoing equation L represents the inductance of shell 33, C the capacity of conductor 3| and R indicates the radiation resistance for each radiating componentI of the antenna.

Throughout the description where the line impedance is mentioned this value has been obtained by the use of the formula Z 138 logmg) where Dv is the inner diameter of the outer tube 33 and d is the outer diameter of the inner conductor M of the concentric line.

It is also desirable to makethe antenna elements of larger diameter than (the transmission line elements of which they are an extension. A most convenient way in which the radiator of large diameter and the central conductor of smaller diameter of the transmission line may be connected is by means of a tapering portion, such yas portion ft2, i3 as shown in Figure 7, or it may be continuously curved as in a horn following an.l exponential, ellipsoidal or other curved law. The

interior surface of the expanding portion when a curved expanding section. is used may be that generated by rotating an ellipse about'an exterior axis parallel to the major axis of the ellipse. The latter shape has been found to 'be more advantageous since it permits a smoother continuation into the ellipsoid shape of the extended centrai conductor. It also permits a smooth rolling over of the sleeve into an elllpsoldal external shape for the lower4 section of the radiator.

Figure 8 illustrates an antenna constructed according to the foregoing. In' this form of the invention an ellipsoidal expansion for the central conductor it of the concentric line has been used. The maximum diameter of the expansion 5| was 8 centimeters.v The overall length of the antenna was 55.5 centimeters or approximately .28 wave-length long. The outer conductor i3 is flared conically or tapered at its inner surface near the antenna, as shown by reference numeral 52, the exposed portion 53 thereof being cylindrical, about centimeters in diameter and 24 centimeters long. Also, conductor lll is gradually expanded to a wider diameter 42 near the elliptical antenna 5|.

In this form of the antenna a concentric transmission line has been used in which the inner diameter of the outer conductor i3 was 2 inches and the outer diameter of the inner conductor Hi was s of an inch which corresponds to aline surge impedance of 110 ohms.

As can be seen by reference to the curves in Figure 9, the modification shown in Figure 8 has a flat characteristic over an even wider frequency range than the arrangement of Figure 5, which was shown in Figure 6.

Referring, now, .to Figure l0, which shows a further modicationof the invention, have discovered that the addition of a metal conductor 5d between the ellipsoidal radiator and the shell 53 is very beneficial. Without this connection the phase relation between the extended portion 5| andthe shell 53 has sometimes too much freedom so .that some irregularities in Ithe impedance may occur Within the desired operating frequency band. Thisl connection 'also is of great grounding of all parts of the antenna. as regards direct current voltages, lightning strokes, etc., and has an additional mechanical benent in that it aids in supporting or guying the somewhat expanded curved conductor 5| rigidly in position. As shown in this figure, the shell portion 53 is also made of a curved cross section 52, 53 which has, been found .to .be beneficial. 'I'he shell 52, 53 is somewhat in the form of a half toroid, the toroid being formed by revolving an ellipse about an exterior axis parallel to the major axis of the ellipse. The lower halt is replaced by a metal base or frustum of a cone |0|2.

The curve in Figure 1l shows the further band width improvement obtained by increasing the diameter of the extension portion 5| to 12 centimeters and approaching a condition where The length of 53 was 24 centimeters and the diameter was increased to 26 centimeters.

As shown in Figure 12 and in the accompanying curve inFigure 13, it has been found further improvement was effected by the further increase in dimensions resulting in a `more perfect fulfillment of the dual requirements of providing a lati() Uf which is constant over as wide a frequency band as possible and also a maximum compensation between capacitive member 5| and inductive member 53. A metal iin 55 of substantial size and cross sectional area was added to provide mechanical support for radiator 5|. A substan- 1 tial fin is more easily compensated for by increased dimensions of the system. This n may be either solid or hollow as desired from a mechanical standpoint. Preferably, it is somewhat circular in cross section at its center portion gradually fairing smoothly into the ellipsoid 5| and the side of the grounded metal shell 53.

From another viewpoint, the introduction of this fin 55 also has the following eiect which should be noted. It constitutes a shunting or parallel current path and thus increases the impedance of the antenna looking into the feed line. This shunt is inductive. One way in which this may be compensated for is by increasing the length of the ellipsoidal extension portion 5|. However, as thismay result in too much deviation from established proportions a more satisfactory way of compensation is by lowering the surge impedance of the line at and towards the mouth of the internally hom-shaped sleeve 52. 'I'his is accomplished by decreasing the ratio of the inner diameter of the outer conductor to the outer diameter of the inner conductor along the length of the transitional portion or tapered section. This results in a decrease of the surge impedance along the length of the expanding portion and the resultant capacity compensates for the increase in inductance caused by fin 55.

Also for adjustment, purposes, the n 55 and antenna 5| may be provided with cylindrical telescoping sections at their central positions and when desired adjustment is reached the parts may be fastened rigidly together by means of set screws, soldering brazing, etc.

In the embodiment shown in Figure 12 and which, upon test had a further improved characteristic as shown by the curve of Figure 13, a

limportance in that it permits of a. metallic center conductor extension 5| has been used having a diameter of 15 centimeters and an overall length of 60 centimeters. The diameter of shell 53 at the top was 18 centimeters between horizontal portions at the extreme top. The diameter at the base was 26 centimeters. The nn 55 was centimeters long between the nearest points of attachment to the ellipsoid and shell and had a diameter of l/m of a centimeter.

Figure la illustrates, partly in cross section, another modification of the invention of Figure 12 in which a larger diameter ellipsoidal central radiator 5| and two supporting ns 55 are used. The minor axis of the ellipsoid 5l in this form is 27 centimeters long and the shell portion 53 was made hernispherical in form. The shell portion 53 in this modication forms with its image, due to ground sheet |2 effectively a half Wave radiator. Auxiliary half horns 52' were provided in this form in order to make the antenna, with its image, the electrical equivalent of a four arm turnstile which will be later described. The proportions of this form proved to have passed the optimum values satisfying the desired conditions already set forth. Even an increase of the diameter of 5| of Figure 12 from l5 to 18 centimeters proved to be in excess of the optimum dimensions although to Va lesser degree than Figure 14. The dimensions of Figure 12 seem to be about the optimum for the frequency band used in the tests. It is, of course, possible that another line of attack may produce an even more perfect dimensional relationship resulting in a still wider band.

In each of the forms of this invention shown in the preceding Figures 8 to 14, the ellipsoidal portion may be either solid or hollow, as desired.

The outer conducting surfaces of the ellipsoids constitute the only portions which are substantially active or effectiverfor transmitting waves or receiving them. A convenient and useful form of construction is to cover a wooden form of the desired shape' with a thin copper foil soldered to form a continuous sheet over the entire surface. f

lFigure 15 illustrates the application of the elementary form of turnstile antenna shown in Figure 14 to a complete turnstile. A central substantially spherical metal portion 53 is supported on a metal pedestal 56 containing the transmission line'. Within the central portion 53 are four inwardly flared sockets forming effectively horizontal horn units 52 whose axes point horizontally in four directions. Within each of these units, 52 and extending outwardly therefrom is a radiating portion 5| Each opposing pair of radiating elements 5| with the central portion 53 constitutes a single half wave antenna. Opposite members of the pairs of radiators 5| are excited in phase opposition and adjacent members in phase quadrature. A rotating eld is thus obtained. The structure for obtaining this phase relationship will be later discussed andl more fully disclosed in subsequent figures.

In order to suppress somewhat the vertical radiation from the antenna the supporting column 56 should be half the length of the opments are arranged to operate as a second an' tenna connected similarly and radiating a rotating eld in the same way as above described. Preferably, the direction of rotation of this field is made opposite to that of the one radiated by the upper antenna in order to reduce coupling between the two antenna. systems. As before, guying conductors or ns 54, two for each antenna element, are provided for stability and grounding of the antennas for lightning strokes.

In a practical embodiment of this modification which would probably be located in. an exposed site, such as at the top of a tall tower or building, such as the Empire State Building, New York City, aviation warning lights 55 and weather instruments 66 could conveniently be mounted at the top of the antenna structure on an extension of pedestal 56. These instruments are, of course, at a neutral or zero potential as far as radio frequency energy is concerned.

While a four arm antenna arrangement in this figure is shown, it is within the scope of this invention to use any number N arms 5|, if necessary, in which case the phase relation of the voltages between consecutive arms 5| will be The modification of this invention shown in Figure 16 is similar to that of Figure 15, except that the relative positions of the two antenna portions 5|, 5| and 6|, 6| have been reversed and both are supported on a supporting column 56'. In this form of construction it is simpler to obtain a circular radiation pattern in the horizontal plane for a pair of antenna due to the fact that the radiating portions of each antenna system are much more closely spaced and less difficulty is had in obtaining the proper space and phase relation between the consecutive radiating portions. Undesired interference patterns yare thus readily avoided. If desired, the two antenna systems may be turned at an angle of 45 degrees with one another on their common axis to further decrease any possible coupling between the two antenna systems. The main uncoupling is, however, provided by the off phase rotation of the antennas.

Since the extreme band width provided by the turnstile antenna is not in all cases necessary, especially for transmitting audio signals, and in order to further decrease any possibility of coupling between the, audio and video antennas, a loop and a turnstile located, as already suggested for two turnstiles in Figure 16, constitute a further improvement `in that these forms of antennae are inherently entirely uncoupled at all frequencies, as will be explained by reference to Figure 17. This diagram illustrates the current X at any given instant in a loop with respect to the currents, indicated by Y, at the same instant obtaining in a turnstile antenna coaxially mounted with respect to the loop. It will be obvious on inspection of the figure that the two antennas are inherently perfectly uncoupled. Since any diametrical conductor is in a neutral position with regard to the field set up by the loop and a turnstile mounted on the axis of the loop has such a position, there will be no coupling between the two antennas.

A modification of this invention utilizing this principle is shown in Figure 18.

In this figure the turnstile antenna is shown at 53. Each element 5| is constructed, as has already been described with reference to Figures and 16, but with closer adherence to optimum proportions as shown in Figure 12. As pointed out before, the optimum dimensions seemingly prevent the use of a spherical hub and in this modication a cross shaped hub, formed by the elements 53, is used. The audio antenna. 10, 1|, 12, which is substituted for the antenna 6|, 6| shown in Figure 16, comprises vfour folded dipole sections bent into a circular form, as shown somewhat more clearly in Figure 20. The principleof this antenna will be more clearly understood by reference to Figure 19.

Figure 19 discloses a folded dipole having a pair of conductors 10, 1|, which are mechanically arranged in parallel planes, conductor 1| being broken at the center and the two wire transmission line Z connected at that point impressing alternating voltages of opposite instantaneous polarity at points e and f. When the length from e to g and from ,f to g is 'half a wave in length, branches 1| and 10 may be considered in parallel, that is, they have a common voltage at ends 12 and are in phase. The impedance between e and f is then approximately four times that of a conventional dipole which has a transmission line insertedat its mid point, or about 288 ohms. A folded dipole of lesser dimensions may also be obtained if the distance from e to g and from f to g is a quarter wave in length. Under this condition the voltage, instead of being a maximum at 12, builds up from point g along the length of the conductor toward point so that a maximum voltage exists between e and f. This corresponds to a very high feed impedance between e and f to transmission line Z. The currents in 1| and f 10 are now to a considerable extent in opposite directions but since they vare not of equal magnitude a resultant field is obtained which causes radiation. Although in this elementary formthe dipole provides a feed impedance which is impractical its lesser dimensions are very attractive in connection with this particular location,

near the video antenna 5|, 53. Tests show that when combining these elements of high feed impedance into a four section circular array, as shown in Figure 20, a mutual effect between the ends 12 of adjacent dipoles was obtained, which substantially lowered the feed impedance between e and f so that it became possible to feed the system with lines of practical dimensions. The resultant impedance due to the mutual reactance of ends 12 is in the order of 220 ohms.

, As already mentioned, the doublets4 being short- 13, each of leads 16 are connected together to the central conductor of transmission -line` 13. In this way a phase diierence of 180 degrees is obtained between conductor 15 and conductor 16. The impedance of each ofthe folded doublets 10, 1| is in the order of 220 ohms and when these are connected 'in parallel to transmission line 13 their effective impedance is in the order of ohms which forms a proper impedance match with the transmission line actually used. At the mid' or voltage nodal points g (Figure 19) metal supporting rods are provided which are fixed and directly connected to the grounded outer shell 11 (Figure 21') thereby supporting the dipoles without affecting *their radio frequency .operation and simultaneously providing a low resistance ground for lightning strokes. Inside of pedestal 56' supporting the audio antenna 10, 1l at a distance equal to one-quarter of the length of the audiocarrier wave below the point of attachment of the antenna to transmission line 13, the transmission line is connected to the interior of the pedestal bya. conductor 11. The quarter wave loop thus formed electrically liberates the top edge of the shell of transmission line 13 by the principle of extremelyhigh impedance at this point caused by connection 11 a quarter wave back. Although transmission line 'i3 is originally nonsymmetric to push-pull load, it can now center itself -to such loading. 'I'he perfection of the centering depends upon how perfect the load is centered or balanced around a neutral which in this case is provided by support 80.

Fig. 21 shows in more detail the connections of both the audio loop and the video turnstile t0 the transmission lines. This figure is partly in section and shows the connection loop for obtaining the degree phase relationship between two adjacent arms of the turnstile video antenna. In order to prevent confusion the other loop which connects to the remaining two arms of the turnstile has not been shown but is exactly similar to the one shown. As can be seen, the central conductor` I4 of the concentric conductor transmission line is connected to the left hand ellipsoidal radiating portion 5| of the turnstile While the other conductor i3 is connected to the end of the tapered portion which attaches to the shell. This transmission line is continued downward a convenient distance and turned back on itself at 8| and connected to the next adjacent arm of the turnstile, extending 'away and in back of the plane of the drawing. To one side of the loop i3, i4, 8|, thus formed is connected the concentric cable transmssionline i3 having an interior conductor i4 at such point that the distance from the point of attachment to one arm of thev turnstile is exactly A oi the length of the operating wave longer than the distance to the adjacent arm of the 'turnstile, This provides the necessary 90 degree phase relationship between the two adjacent arms and has another and further advantage when the line isproperly matched. In the case of such a transmission line if either a capacitive or an inductive reactance, which is fairly high compared to the surge imy edance of the line, is added across the transmission line, its reactance may be perfectly compensated for by the addition of another and exactly equal reactance at a spacing of an odd multiple of a quarter wave therefrom. Thus, in the antenna, any residual reactance in one arm of the lturnstile is exactly compensated for by a similar reactance of the next adjacent arm of the turnstile to which it is connected through the phasing loop.

The application of this principle, as shown in Figure 21, increases the band width antenna of the turnstile elements which have the already exceptional band width of approximately 20% with a reilection of or less to approximately 30% with the same amount of reection. At the point of attachment oi' concentric cable I3', I 4' to the phasing loop I3. Il a slightly enlarged portion 18 is provided on the inner conductor I4. This is to compensate forrthe change in impedance in the transmission line due to the aperture in casing I3 where casing I3' is attached and through which conductor I4 passes. The transmission line I 3', I4' is fed by one phase. The other two arms of the turnstile are connected ln an exactly similar manner and are fed by the opposite phase of the video transmitter. Of course, it is to be understood that line I3', I4 must have a surge impedance half that of I3. I4.

As shown in Figure 21, additional support for radiator 5I is supplied by means of insulator 53 in the throat of the expansion portion of the antenna. In order to prevent rain, snow, etc., from running into the expansion a horn portion, a semicircular rainshield 5'I is attached to the top of shell 53 and immediately behind it and attached to the radiator 5I is an annular shield 58. These two shields 5l and 58 are formed of insulating material. If desired, electric heating elements may be incorporated within radiators 5I, arms 55 and the shell 53 in order to melt accumulations of sleet in severe Weather.

Figure 22 shows diagrammatically the complete connection of all four arms of the turnstile antenna. to the push-pull output of the video transmitter. In order to simplify the disclosure the outer shells of the transmission lines have not been shown.

By changing both transmission lines I3', I4 to a position diametrically opposite on the phasing loops, as indicated by R, R (Figure 22), the phase rotation field produced by the antenna may be reversed.

Figure 23 illustrates curves showing the extreme band width obtained with the turnstile antenna 5I, 53 constructed according to Figure 18. 'I'hese curves were taken using a reference wave length of 225 centimeters. The curve in solid lines was made when my antenna was rst constructed and the curve in dotted lines illustrates the improvement obtained after correcting the transmission line to match the antenna more perfectly. Some of the other important dimensions of the antenna used, whose characteristic is shown by the curve of Figure 23, are as follows: The length of the minor axis of the ellipsoid 5I was 15 centimeters. The length of the major axis of each of the ellipsoids 5| was 41 centimeters. The diameter of the shell portions at their extreme ends was 18 centimeters, and the maximum diameter of portion 53 was 26 centimeters. The length from the center of the hub to the end of 53 was 29 centimeters. Using the modied form of the supporting member, as shown by 55 in Figiue 18, in order to obtain maximum mechanical strength and retain the desirable electrical features, the maximum diameter of the supporting arm was increased to 1.3 centimeters at its central portion and about ,95 of a centimeter in each of the stirrup portions 55". The arm 55" was attached to each ellipsoid 17 centimeters from the end of shell 53 whilef the point of attachment of the arm to shell 53 was 8 centimeters in from the end of the shell.

As can be seen byan inspection of the curve in Figure 23 the band width with less than 5% reection is so broad that it is entirely feasible to transmit two complete television programs over a single antenna. This may be conveniently done by an arrangement as schematically shown by block diagrams in Figures 24 and 25. If it is desired to use only a single antenna, as shown in Figure 24, the ilrst video transmitter IOI and its corresponding audio transmitter |02 are iirst fed separately into a separating filter network |03 and there combined into a single channel |04. Likewise, thesecond video transmitter 20| and its corresponding audio transmitter 202 are fed separately into the separating lter 203 and there combined into a. single channel 204. These two channels are then combined by iilter |05 into a single channel |06 and applied to the single turnstile antenna. If it is desired to transmit the video signals over one antenna and the audio signals over the other, as in Figure 18, except that two complete programs are radiated, it may be done as in Figure 25, which shows the ilrst audio transmitter |02 and the second audio transmitter 202 fed into a filter 2|3 and thence to the audio antenna "I0, 1I. At the same time the ilrst video transmitter IOI and the second video transmitter 20| have their outputs combined in the filter II3 and the combined output is applied to the video turnstile antenna 5I, 5I of Figure 18.

Any of the antennas described may be used for receiving as well as for transmission.

Moreover, the turnstile antenna, as shown in Figures 15, 16, 18 and 21 may be combined with a vertically polarized antenna as shown in any of Figures 5 to l2, inclusive, mounted centrally thereabove. An antenna constructed according to this concept is shown in Figure 26. Since each part has been separately described in detail, it is believed unnecessary to describe the combination which should be clearly understood from an inspection of the ligure.

Also, I may construct a plurality of half wave antennae according to the principles heretofore set forth and arrange them in a common horizontal plane about a central point and lying along tangents equidistantly spaced about a circle having its center at that point. 'I'he characteristics of an antenna. having its radiating members thus arranged have been disclosed in my co-pending application No. 76,745, filed April 28, 1936, now Patent No. 2,131,108. The adaptation of the present antenna to such construction is shown in Figure 27.

Furthermore, any of the antennae or combinations thereof, heretofore described, may be mounted within a metal paraboloid at the focus thereof for directional signalling.

It should be clearly understood that the theory of operation outlined heretofore in this specification is given only by way of explanation and that while it is believed to be substantially accurate the invention is not dependent upon the absolute accuracy of the theory expressed but may also be practiced emperically from the ilnite values, also heretofore given.

It should also be clearly understood that while I have particularly shown and described several modications of the invention, the invention is not to be limited thereby but may be modified without departing from the spirit and scope thereof.

We claim: Y

l. An antenna system comprising a number N of radiating elements disposed 'radially about a central point in a common horizontal plane, each radiating element spaced substantially degrees from adjacent radiating elements, each of said radiating element comprising a central conductor element having a transverse dimension which is a large fraction of the operating Wave and an outer shell surrounding a portion of each of said conductors at their adjacent ends, said central conductor extending radially outward beyond the end of said outer shell, the over-all length oi' each of said radiating elements including the exposed portion of said central conductor and the over-all length of the shell being substantially equal to a quarter of the length of the operating wave, the capacitive reactance C or" said exposed portion and' the inductive reactance L of said shell portion being so related that as nearly as possible approaches R, the radiation resistance of each component of said antenna.

2. An antenna system comprising a number N of radiating elements disposed radially about a central point in a common horizontal plane, each radiating element spaced substantially en N degrees from adjacent radiating elements, each of said radiating elements comprising a central conductor element having a transverse dimension which is a large fraction oi the operating wave and an outer shell surrounding a portion of each of said conductors at their adjacent ends, said central conductor extending radially outward beyond the end of said outer shell, the overall length of each of said radiating elements including the exposed portion of said central conductor and the over-all length of the shell being substantially equal to a quarter'of the length of the operating Wave, the capacitive reactance C of said exposed portion and the inductive reactance L of said shell portion being so related that as nearly as possible approaches R, the radiation resistance of each component of said antenna, and means for maintaining radio frequency voltages on said conductors, the phase relation between the voltages on adjacent conductors being m N electrical degrees.

3. An antenna system comprising a number N of radiating elements disposed radially about a central point in a common horizontal plane, each radiating element spaced substantially an N degrees from adjacent radiating elements, each of said radiating elements comprising a central cylindrical conductor element having a diameter which is a large fraction of the length of the operatlng wave and an outer shell surrounding a portion of each of said conductors at their adjacent ends, said central conductor extending radially outward beyond the end of said outer shell, the over-all length of each of said radiating elements including the exposed portion of said central conductor and the over-all length oi the shell being substantially equal to a quarter oi.' the length of the operating Wave, the capacitive reactance C of said exposed portion and the inductive reactance L of said shell portion being so related that as nearly as possible approaches R, the radiation resistance of each component ci said antenna.

4. An antenna system comprising a number N of radiating elements disposed radially about a central point in a common `horizontal plane, each radiating element spaced substantially en N degrees from adjacent radiating elements, each of said radiating elements comprising a central cylindrical conductor element having a diameter which is a large fraction of the length of the operating Wave and an outer shell surrounding a portion of each of said conductors at their adjacent ends, said central conductor extending radially outward beyond the end of said outer shell, the over-all length or" each of said radiating elements including the exposed portion of said central conductor and the over-all length of the shell being substantially equal to a quarter of the length of the operating wave, the capacitive reactance C of said exposed portion and the inductive reactance L of said shell portion being so related that as nearly as possible approaches R, the radiation resistance of each component of said antenna, and means for maintaining radio frequency voltages on said radiating elements, the phase relation between the voltages on adjacent radiating elements being that as nearly as possible approaches R, the radiation resistance of each component of said antenna.

6. An antenna system comprising a number N of radiating elements disposed radially about a ai N degrees from adjacent radiating elements, each oi' said radiating elements comprising a cylin-` drical conductor element and an outer shell surrounding a portion of each of said conductor elements at their adjacent ends, said central conductor extending radially outward beyond the end of said outer shell, the over-all length or each of said radiating .elements including the exposed portion of said central conductor and the over-al1 length of the shell being substantially equal to a quarter of thelength of the operating wave, the capacitive reactance C of said exposed portion and the inductive reactance L of said shell portion being so related that degrees from adjacent radiating elements, each of said radiating elements comprising a cylindrical conductor element and an outer shell sur- 4 rounding a portion of each of` said conductor elements at their adjacent ends. said central conductor extending radially outward beyond the end of said outer shell, the over-al1 length of each of said radiating elements including the exposed portion of said central conductor and the over-all length of the shell being substantially equal to a quarter of the length of the operating wave, the capacitive reactance C of said exposed portion and the inductive reactance L of said shell portion being so related that as nearly as possible approaches R, the radiation resistance of each radiating element of said antenna, each radiating element having a diameter which is large in terms of the length of the operating wave near the center of said antenna and which decreases along the length of said radiating element with increasing distance from saidi center, and means for maintaining radio frequency voltages on said radiating elements, the phase relation between the voltages on adjacent radiating elements being an N electrical degrees.

8. An antenna system comprising four radiating elements disposed radially about a central point in a common horizontal plane, each radiating element spaced substantially 90 degrees from adjacent radiating elements, each of said radiating elements comprising a conductor having a circular cross-section and an outer shell surroundshell being substantially equal to a quarter of the lengthV of the operating wave, the capacitive reactance C of said exposed portion and the inductive reactance L of said shell portion being so related that as nearly as'possible approaches R, the radiation resistance of each of said radiating elements, each radiating element having a diameter which is large in terms of the length of the operating wave near the center of said antenna and which decreases along the length of said conductor with increasing distance vfrom said center, and means for maintaining radio frequency voltages on said radiating elements, the phase relation between the voltage on adjacent radiating elements being electricaldegrees.

9. An antenna system comprising a quarter wave aerial conductor element having a transverse dimension which is a large fraction of the length of theY operating wave near the neutral voltage plane of said antenna and decreases along the length of said conductor with increasing distance from said plane, a concentric conductor transmission line and means for coupling said line to said conductor element comprising a tapered concentric conductor section having a central conductor and an outer shell surrounding said conductor, the ratio of the diameter of said conductor and shell being constant through the length of said tapered section whereby a gradual 0 transition between'saidv transmission line and said antenna is attained without material change in the linesurge impedance.

10. An antenna system comprising a number N of quarter Wave aerial conductor elements having 5 lateral dimensions which are large in terms of the length of the operating wave and disposed radially about a central point and in a common horizontal plane, each conductor spaced substantially en N degrees from adjacent conductors and means for maintaining radio frequency voltages on said conductors, the phase relation between the voltages on adjacent conductors being in N electrical degrees, said means comprising a concentric conductor transmission line and means for couplingsaid line to each of said conductor elements comprising a number N of tapered concentric conductor sections, each having a central conductor expanding into said aerial conductor elements and an outer shell surrounding said conductor, the ratio of the diameter of said conductor and shell. being constant through the length of said tapered section whereby a gradual transition between said transmission line and said antenna is attained without material change in the line surge impedance.

11. An antenna system comprising a number N of quarter Wave aerial conductor elements having a circular'cross section and disposed radially about a central point in a common horizontal azsavac plane. each conductor having a diameter which is large in terms oi the length of the operating y wave near the center of said antenna and which decreases along the length of said conductor with increasing distance from said center, each conductor being spaced substantially en N an N

electrical degrees, said means comprising a concentric conductor transmission line and means for coupling said line to each of said conductor elements comprising tapered concentric conductor sections each having a central conductor of the samediameter as the conductor oi the concentric line to which it is connected and an outer shell surrounding said conductor, the ratio of the diameter of each ci said conductors and shells being constant through the length of said tapered sections whereby a gradual transition between said transmission iine and said antenna is attained without material change in the line surge' impedance.

l2. in antenna system comprising four quarter wave conductor elements disposed radially about' a central point and in a common horizontal plane, each conductor spaced substantially 90 degrees irom adjacent conductors, each conductor having a diameter which is large in terms of the length ci the operating wave near the center of said antenna and which decreases along the length of said conductor with increasing distance from said center and means i'or maintaining radio frequency voltages on said conductors, the phase relation 'between the voltages onadjacent conductors being' equal to 90 electrical degrees, said means comprising a concentric conductor transmission line and means for coupling said line to each oi said conductor elements comprising tapered concentric conductor sections, each having a central conductor of the same diameter as the conductor ci the concentric line to which it isAv connected and an outer shell surroundin7 said conductor, the ratio of the diameter of said conductor and shell being constant through the length ci' said tapered section whereby a gradual transition between said transmission line and said antenna is attained Without material change in the line surge impedance.

13. An antenna system comprising four quarter wave conductor elements disposed radially about a central point and in a common horizontal planej each conductor spaced substantially 90 degrees from adjacent conductors and means for maintaining radio frequency voltages on said conductors, the phase relation between the voltages on adjacent conductors being equal to 90 electrical degrees and a reilector parallel to said plane and spaced therefrom a distance the order of a half wave length whereby maximum cancellation occurs between the wave radiated from said conductors in a direction away yfrom said F reflector and the wave reflected from said reilector.

14. An antenna system comprising a number N of quarter wave conductor elements disposed radially about a central point and in a common horizontal plane each. conductor spaced substantially degrees from adjacent conductors and means .for maintaining the radio frequency voltages on said conductors, the phase relation between the voltages on adjacent conductors being equal to an N electrical degrees and a redentor parallel to said common horizontal plane and spaced therefrom a distance the order of a half wave length whereby maximum cancellation occurs between the wave radiated from said conductors in a direction away from said redactor and the wave reected from said reector.

15. An antenna system comprising four quarter wave conductor elements disposed radially about a central point and in a common horizontal plane, each conductor spaced substantially degrees from adjacent conductors, each. conductor having a diameter which is large in terms of the length of the operating .wave near the center of said antenna and which decreases along the length oi said conductor with increasing distance from said center and means for maintaining radio frequency voltages on said conductors, the phase relation between the voltages on adiacent/conductors being equal to 90 electrical degrees, said means comprising a concentric conductor transmission line and means for coupling said line to each of said conductor elements comprising tapered concentric conductor sections, each having a central conductor of the same diameter as the conductor of the concentric line to which it is connected and an outer shell surrounding said conductor, the ratio of the dlam- 16. An antenna system comprising a central conductor and an outer shell surrounding said conductor, said central conductor extending beyond the end of said outer shell, a concentric cable transmission line connected to said conductor and shell and forming a continuation thereof and means forming a neutral voltage plane at the junction of said shell with said line. the transverse .dimension ofsald central conductor being large in terms of the length of the operating Wave at the neutral plane and decreasing along the length of said antenna with increasing distance from said plane, and a conductive support connected between the end of said central conductor and said outer shell, said connection acting as an inductance connected between said conductor and said shell.

1'7. An antenna system comprising a central conductor and an outer shell surrounding said conductor, said central conductor extending be- "yond the end of said outer shell, a concentric the transversedimension of said central conductor being large in terms of the length oi' the operating wave at the neutral plane and decreasing along the length oi said antenna. with increasing distance from said plane, and a conductive support connected between the end of said central conductor and said outer shell, said connection acting as an inductance connected between said conductor and said shell, and means ,shell surrounding said conductor, said central conductorextending beyond the end of said shell,

a concentric cable transmission line and means for coupling said line at said central point to each of said elements, said means comprising a tapered concentric conductor section `having a central conductor and an outer'shell surrounding said conductor, the ratio ofthe diameter of said conductor and shell being constant through the length of said outer section whereby a gradual transition between said transmission line and said antenna is attained without material change in the line surge impedance.

19. An antenna system comprising a plurality of radiating elements disposed radially in a common plane about a central neutral point, each of said elements formed of a central conductor having a transverse dimension large in terms of `the length of the operating wave, and an outer shell surrounding said conductor, said central conductor extending beyond the end of said shell, a concentric cable transmission line and means Within said outer shell for coupling said line at said central point to each of said elements, said means comprising a tapered conductor connected to said central conductor and the ratio of the diameters of said tapered conductor and the interior of said shell being constant through their length whereby a gradual transition betWeensaid transmission line and said antenna is attained without material change in the line surge impedance, and a conductive support connected between the central conductor and the shell of each of said radiating elements, said connection acting as an inductance connected therebetween.

20. An antenna system comprising a number N of radiating elements disposed radially in a common plane about a central neutral point, each of said elements formed of a central conductor having a transverse dimension large in terms of the length of the operating wave, and an outer shell surrounding said conductor, said central conductor extending beyond the end of said shell, each conductor spaced degrees from adjacent conductors and means for maintaining radio frequency voltages on said conductors, the phase relation between the voltages on adjacent conductors being equal to electrical degrees, said means comprising a concentric cable transmission line and means within said outer shell for coupling said line at said central point to each of said elements, said means comprising a tapered conductor connected to said central conductor, the ratio of the diameters of said tapered conductor and the interior of said outer shell being constant through their length whereby a gradual transition between said transmission line andv said antenna is attained without material change in the line surge impedance, and a conductive support connected between the central conductor and the shell of each ot said radiating elements, said connection acting as an inductance connected therebetween, and capacitive means connected between the elements of said coupling means for compensating for said increase in inductance.

21. An antenna system comprising a plurality of radiating elements each of said elements having a transverse dimension large in terms of the length of the operating wave and disposed radially in a common plane about a central neutral point, each of said elements formed of a central conductor and an outer shell surrounding said conductor, said central conductor extending beyond the end of said shell, and a conductive support connected between the end of said central conductor and said shell of each of said radiating elements, said connection acting as an inductance connected therebetween, a concentric cable transmission line and means for coupling said line at said central point to each of said elements within said outer shell, said means comprising a tapered conductor connected to said central conductor, the ratio of the diameters of the tapered conductor and the interior of the outer shell increasing along the length of said means whereby the increase in inductance caused by said conductive support is compensated.

22. An antenna system comprising a plurality of ellipsoidal radiating elements disposed radially in a common plane about a central neutral point, each of said elements formed of a central conductor having a transverse dimension large in terms of the length of the operating wave, and an outer shell surrounding said conductor, said central conductor extending beyond the end of said shell, a concentric cable transmission line and means for coupling said line at said central point to each of said elements, said means comprising a tapered concentric conductor section having a central conductor and an outer shell surrounding said conductor, the ratio of the diameter of said conductor and shell being constant through the length of said outer section whereby a gradual transition between said transmission line and said antenna is vattained without material change in the line surge impedance.

23. An antenna system comprising a plurality of ellipsoidal radiating elements disposed radially in a common plane about a central point, each of said elements formed of a central conductor having a transverse dimension large in terms of the length of the operating wave and an outer shell surrounding said conductor, said central conductor extending beyond the end of said shell, a concentric cable transmission line and means within said outer shell for Acoupling said line at said central point to each of said elements, said means comprising a tapered conductor connected to said central conductor, the ratio of the diameters of said tapered conductor and the interior of said shell being constant through their length whereby a gradual transition between said transmission line and said antenna is attained without material change in the line surge impedance, and a conductive support connected between the cenmaar degrees from adjacent conductors and means for maintaining radio frequency voltages on said conductors, the phase relation between the voltages on adjacent conductors being equal to ne N electrical degrees, said means comprising a concentric cable transmission line and means within said outer shell for coupling said line at said central point to each of said elements, said means comprising a tapered conductor connected to said central conductor, the ratio oi the diameters of said tapered conductor and the interior of said outer shell being constant through their length whereby a gradual transition between said trans# mission line and said antenna is attained without material change in the line surge impedance, and a conductive support connected between the central conductor and the shell of each o said radiating elements, said connection acting as an inductance connected therebetween, and capacitive means connected between the elements of said .coupling means for compensating for said increase in inductance. h'

25. An antenna system comprising a plurality of ellipsoidal radiating elements each of said elements having a transverse dimension large in terms of the length of the operating wave and disposed radially in a common plane about a central neutral point, each of said elements formed of a central conductor and an outer shell surrounding said conductor, said central conductor extending beyond the end ci said shell, and Aa conductive support connected between the end of said central conductor and said shell of each of said radiating elements, said connection acting as an inductance connected therebetween, a concentric cable transmission line and means within said outer shell for coupling said line at said central point to each of said elements, said means comprising a tapered conductor connected to said central conductors, the ratio of the diameters of the tapered conductor and the interior of the outer shell increasing along the length of said means whereby the increase in inductance caused by said conductive support is compensated.

26. An antenna system comprising a plurality of antennas each including a number N of quarter wave conductor elements having lateral dimensions which are large in terms of the length of the operating wave and disposed radially about a central point in a common plane, each conductor spaced substantially degrees from adjacent conductors and means for maintaining radio frequency voltages on said conductors, the phase relation @tween the voltages on adjacent conductors being sa N electrical degrees. said antennas being located in parallel planes and having their central points on a common axis perpendicular to said planes, the corresponding conductor elements of adjacent antennas being so energized from semrate energy sources for each antenna that opposing phase rotations are obtained.

27. An antenna system comprising a plurality of antennas each including a number N of quarter wave cylindrical conductor elemente having a diameter which la large in terms ci' the length of the operating wave and disposed radially about a central point in a common plane, each conduc tor spaced substantially se' N degrees from adjacent conductors, said antennas being located in parallel planes and having their central points on a common anis perpendicular to said planes, said antennas being energized in an in phase relationship.

2t. .an antenna system comprising a plurality oi antennas each including a number N oi quern ter wave conductor elements having a circular cross-section and disposed radially about a central point in a common horizontal plane, earch conductor having a diameter which is large in terms of the length of .the operating wave near the center oi said conductor and which decreases along the length of said conductor with increasing distance from said center, each conductor being spaced substantially an N degrees from adjacent conductors, and means for maintaining radio frequency voltages on said conductors, the phase relation between the voltages on adjacent conductors being ne N electrical degrees, said antennas being located in parallel planes and having their central points on a common axis perpendicular to said planes, said antennas being energized in an opposing phase relationship.

29. An antenna system comprising a plurality of antennas as dened in claim ll, located in parallel planes and with their central points on a conmon axis perpendicular to said plane, said antennas being energized for opposing phase rotation from dierent energy sources.

30. An antenna system comprising a plurality of antennas as dened in claim 20, located in parallel planes and with their central points on a common axis perpendicular to said planes, said antennas being energized for opposing phase rotation from dierent energy sources.

31. An antenna system comprising a plurality of antennas as deined in claim 23, located in paryallel planes and with their central points on a common axis perpendicular to said planes, said antennas being `energized for opposing phase rotation from dierent energy sources.

32. An antenna system comprising a plurality of antennas each including a number N of quarter wave conductor elements having-lateral dimensions which are large in terms of the length ductors, the phase relation between the of the operating wave and disposed radially about a central point lin a common plane, each conductor being spaced substantially sa! N parallel planes and having their central points on a common axis perpendicular to said planes,

' said antennas being so energized from separate energy sources for each antenna that opposing phase rotations are obtained, the elements of one antenna being arranged to bisect the projected angles formed by the elements of the adjacent antenna.

33. An antenna system comprising a plurality of antennas each including a number N of quarter wave cylindrical conductor elements having a diameter which is large in terms of the length of the operating Wave and disposed radially about a central point in a common horizontal plane, each conductor being spaced substantially degrees from adjacent conductors, and means for maintaining radio frequency voltages on said convoltages on adjacent conductors being quarter Wave conductor elements having a circular cross-section and disposed radially about a central point in a common horizontal plane, each conductor element having a diameter which is largel in terms of the length of the operating Wave near the center of said antenna and which decreases along the length of said conductor with increasing distance from said center, each conductor being spaced substantially degrees from adjacent conductors, and means for maintaining radio frequency voltages on the conductors of each of said antennas, the phase relation between the `voltages on adjacent conductors being sa N ` electrical degrees, said antennas being located in parallel planes and having their central point on a common axis perpendicular to said planes, said antennas being energized for opposing phase rotation from separate energy sources, the elements of one antenna being arranged to bisect the projected angles formed by the elements of the adjacent antenna.

35. An antenna system comprising a plurality of antennas as defined in claim 11, located in parallel planes and with their central points on a common axis perpendicular to said planes, the elements or one antenna arranged to bisect the projected angles formed by the elements of the other antenna.

36. An antenna. system comprising a plurality of antennas as defined in claim 20, located in parallel planes and with their central points on a common axis perpendicular to said planes, the elements of one antenna arranged to bisect the projected angles formed by the elements of the other antenna.

37..,An antenna system comprising a plurality of antennas as defined in claim 23, located in parallel planes and with their central points on a common axis perpendicular to said planes, the elements of one antenna arranged to bisect the projected angles formed by the elements of the other antenna.

38. A horizontal loop antenna comprising four dipole antennae forming a circle, each dipole comprising a pair of conductors arranged in closely spaced parallel planes and each bent in an arc of a circle, means for connecting the conductors of each dipole together at their extreme ends, one conductor of each pair being broken at its mid point forming a pair of adjacent ends, a concentric cable transmission line and means for connecting the central conductor of said line to one of the adjacent ends of each dipole and means for connecting the casing of said transmission line to theother of the adjacent ends of each dipole antenna.

39. A television antenna system for simultaneous transmission oi video and audio signals on closely adjacent frequencies without interference comprising a turnstile antenna energized by one of said signals and a loop antenna energized by the other of said signals, said antennas being located in parallel horizontal planes, and means for supporting said antennas with their central points on a common axis perpendicular to said planes. i

40. An antenna system for simultaneous transmission oi a pair of signals on closely adjacent frequencies without interference comprising a turnstile antenna comprising a number N oi' quarter Wave conductor elements having lateral dimensions which are large in terms of the length of the operating Wave and disposed radially about a central point in a common horizontal plane, each conductor spaced substantially degrees from adjacent conductors, and means for maintaining radio frequency voltages on said conductors representative of one of said signals, the phase relation between the voltages on adjacent conductors being electrical degrees, and a loop antenna energized by the other of said signals comprising four dipole antennae forming a circle, each dipole comprising a pair of conductors arranged in closely spaced parallel planes and each bent in an arc of a circle, means for connecting the conductors of each dipole together at their extreme ends, one conductor of each pair being broken at its 

